The present invention relates to a process for the determination of the pressure prevailing in a fuel injection manifold of an internal combustion engine and a corresponding device.
More particularly, it relates to evaluating the fuel pressure when the pressure sensor works under boundary conditions, particularly at startup.
It is already known to measure the pressure prevailing in the fuel injection manifold of an internal combustion engine. To this end, a pressure sensor is emplaced in this injection manifold.
In an engine with conventional indirect injection, this injection pressure is relatively low, of the order of 3 to 5 bars. On the other hand, in the case of an engine with direct injection, this pressure is high and generally varies from 30 to 120 bars. Of course, pressure sensors specifically adapted to measure high pressures are used. At these high pressures, these sensors generally have a precision of the order of xc2x13%, which is sufficient to control correctly the quantity of fuel to be injected into the cylinder of the engine.
However, during startup, the injection manifold is not immediately supplied with fuel at a pressure of 30 to 120 bars. Thus, these pressures are achieved by the mechanical pump driven by the engine and are not reached until the pump has a speed of rotation of the order of 200 to 300 rpm. This speed of rotation is not reached immediately upon startup. Thus, between the startup phase of the engine (0 rpm) and the pressurized phase (200 to 300 rpm), the pressure in the injection manifold varies and increases progressively as a function of the speed of rotation of the vehicle motor.
To assist startup of the vehicle, it is known to use a feeding pump whose object is to supply the engine with fuel having a pressure of at least 3 to 5 bars during startup. This feeding pump improves the startup of the engine but does not permit the pressure sensor to operate with high precision during startup. Thus, the pressure sensor is not capable of indicating the real pressure in the injection manifold when the latter varies from 3 to 30 bars. This sensor is designed to work with high precision between 30 and 120 bars, but at low pressure, it has considerable errors of the order of xc2x1200%. It is thus impossible to rely on the values of pressure indicated by the sensor when the pressure is below 30 bars. However, as the regulation of the pressure in the pressure manifold is carried out by electronic control of the leakage of a proportional regulator which is itself in a loop with the measurement given by the pressure sensor, if the measurement of the sensor is erroneous and the opening time of the injectors is corrected as a function of the supply pressure so as to control the maximum flow rate thereof, the regulation of the fuel pressure is impossible. The same is true for controlling the quality of the startup.
Moreover, it is not possible to establish a typical law of development of the pressure prevailing in a given fuel supply system during the startup phase, because the latter varies as a function of the development of the engine speed and is never the same.
The fact of not being able to determine with precision the development of the fuel pressure during startup, gives rise to numerous drawbacks, namely more or less long startups, variations in the performance of startup, stalling after startup . . . etc.
The object of the present invention is to overcome all of these drawbacks and particularly to evaluate the development of the fuel pressure during startup of an engine with direct injection.
To this end, the present invention relates to a process for determining the pressure prevailing in a fuel injection manifold of an internal combustion engine, said motor being particularly provided with:
a pressure sensor mounted in the injection manifold, said sensor being adapted to operate with maximum precision between a lower limit and an upper limit of pressure,
a pump for pressurizing the fuel,
a feeding pump supplying the circuit with fuel at a feeding pressure below the lower limit of the range of maximum precision of the sensor, and
a pressure regulator, said process being characterized in that it consists in:
axe2x80x94supplying the feeding pump with fuel, such that the injection manifold will be supplied with fuel at the feeding pressure,
bxe2x80x94measuring the pressure prevailing in the injection manifold with the pressure sensor, when the fuel is at the feeding pressure,
cxe2x80x94deducing the percentage of error of the pressure sensor, and memorizing this error,
dxe2x80x94establishing a law of linear decrease of this error between the feeding pressure and the lower limit of the range of maximum precision of the sensor and
exe2x80x94deducing for each value of pressure measured by the sensor between the feeding pressure and the lower pressure limit, the real value of the pressure of the fuel in the injection manifold, to correct the quantity of injected fuel.
Thus, knowledge of the measuring error of the sensor at the feeding pressure permits evaluating the real pressure in the injection manifold when this pressure is comprised between the feeding pressure and the lower limit of the range of precision of the sensor. Thus, the linearization of this error, between the feeding pressure and the lower limit of pressure, permits establishing the law for computing the real pressure (law of correction of the measurement of the sensor) between the two pressure values. Thus, the measurements carried out by the sensor beyond its maximum precision zone are nevertheless usable, after application of the correction law determined by linearization.
Preferably, such a process of evaluation of the pressure can be used at the startup of the vehicle and/or the stopping of this latter. Thus, for example, the error value determined at startup can be confirmed at stopping.
Similarly, the law of correction of the measurement of the sensor can be determined during initial driving. At each further stop, it then suffices to verify that the error of measurement at the feeding pressure is always the same. In this case, it is not necessary to repeat the measurement of this error at each startup.